Grass mowing machines for cutting grass on golf courses or other areas that require high quality cutting such as parks and athletic fields, may include a plurality of cutting units. Each cutting unit may be attached to the outer end of a lift arm extending laterally outwardly from a traction vehicle. Each cutting unit may be a reel-type cutting unit with a generally horizontally-aligned cutting reel, and front and/or rear rollers that support or carry the cutting unit across the surface of the ground during mowing. Blades of the rotating reel interact with a bedknife to cut grass with a scissoring action. Alternatively, each cutting unit may be a rotary cutting deck with a blade rotating on a generally vertical axis under a deck.
Grass mowing machines may include implement lift systems to raise and lower the cutting units on the outer ends of the lift arms. Implement lift systems for mower cutting units may include hydraulic cylinders connected to the lift arms. For example, a hydraulic cylinder attached to a lift arm may be extended to raise a cutting unit to a transport or service position, and retracted to lower the cutting unit to a mowing position. Examples of grass mowing machines with hydraulic implement lift systems for mower cutting units are provided in U.S. Pat. Nos. 5,297,378 and 5,343,680.
Alternatively, grass mowing machines may have implement lift systems for mower cutting units that include electric motors and linear actuators to raise and lower the cutting units. For example, an electric motor may drive a linear actuator such as a ball screw assembly and shaft attached to a lift arm to an extended position to raise a cutting unit, or to a retracted position to lower a cutting unit. Examples of mowing machines having electric implement lift systems for mower cutting units are shown in U.S. Pat. Nos. 5,540,037 and 5,553,445.
It is highly desirable to use an electric implement lift system for mower cutting units, especially on mowing machines with electric traction and implement drive. However, electric implement lift systems with linear actuators are not sufficiently durable, nor are they sufficiently reliable, to repeatedly raise and lower large cutting units weighing more than about 100 pounds each. Additionally, electric implement lift systems with linear actuators may not have sufficient input torque to raise and hold or lock a cutting unit in a raised/transport or service position.
An electric implement lift system for mower cutting units is needed that is durable and reliable enough to repeatedly raise and lower large cutting units weighing over about 100 pounds. An electric implement lift system for mower cutting units is needed that will not require input torque from a motor to hold or lock a cutting unit in the raised/transport or service position.